It's a small, small, small world
Remember how proud you felt when you showed everyone you could ride a two-wheeler? That's how proud Krystyn Van Vliet acts as she opens the door to a large stainless-steel instrument at the NanoMechanical Technology Laboratory at the Massachusetts Institute of Technology.Skip to next paragraph
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"This is a nano-indenter," says Ms. Van Vliet, a material science graduate student at MIT in Cambridge, Mass. Then she points to a tiny, diamond-tipped needle inside. "We take a sample of the new material we are testing and push that diamond into the sample."
If the material is strong, the diamond will hardly break the surface. If it's soft, the tip might poke a hole in it.
Researchers need to know how strong a new material is before they can use it for soldiers' uniforms, computer chips, cars, or airplanes.
But it isn't easy to test a portion of material that is one hundred-thousandth smaller than a strand of your hair. How small is that? It's a billionth of a meter a nanometer. Samples are so tiny because scientists need to find out how materials behave at that size. Remember, they are building very small structures.
So Van Vliet, fellow graduate student Yoonjoon Choi, and others study new "nanomaterials" in the new NanoLab.
With its floor-to-ceiling glass walls and two projection screens that display nano-structures to passersby on a busy campus hallway, the lab itself is a teaching aid for students. This new science needs to be better known.
"Many people have never heard of 'material science and engineering,' " Van Vliet says. "When I tell people that I am a material scientist, they sometimes assume that I design fabrics." So what does she do? "I study how materials behave," she says.
"When you are building a bridge, you need to know how strong the material is that you are going to use," Van Vliet says. So scientists put the material, often metal, through a series of tests: They pull it, bend it, and stretch it until it breaks. From the tests, scientists learn the strength of a material and how much they will need to build a safe bridge or other structure.
But when testing materials at the teeny-weeny level for use in computers, music CDs, and other items, the samples are too small to pull and stretch. Instead, you poke.
Using the nano-indenter, Van Vliet measures two things: the "load" (force) being pushed into the sample and how deeply the diamond point goes into it.
"Measuring those two things while we are pushing in and pulling out the diamond indenter," Van Vliet says, "gives us enough information to calculate how stiff the material is, how strong it is, when it will fracture, and how much load it will take before it permanently deforms [breaks]." If the material is strong, the diamond tip won't go in very far. If it's soft, the tip might make a deep dent.
Meanwhile, Mr. Choi stares at rows of orange hills and valleys on a computer monitor. A large yellow spike occasionally interrupts the scene.
"These spikes are defects in the sample," Mr. Choi says. "I'm looking for a piece of copper with no defects."
To find his perfect copper sample, Choi uses an atomic-force microscope (AFM).
A traditional optical microscope makes an image using reflected light. The atomic-force microscope touches the sample with very small forces. It contains a special "piezo crystal" that gets bigger or smaller as electrical current runs through it. As the crystal changes size, it moves "a cantilever [or beam] that looks like your finger, with a sharp point at the end," Van Vliet says. The cantilever moves along the sample's surface and makes a picture of the microscopic mountains and valleys on a sample's surface. It maps the topography of the sample.
The AFM is so sensitive that Choi can measure features that are only nanometers (billionths of a meter).
The NanoLab currently has three nano-scale machines: the atomic-force microscope and two diamond-tipped nano-indenters. The machines are quite large, but most of their bulk is insulation, to keep the needle from vibrating when people walk nearby. "We are trying to measure such tiny distances," Van Vliet says, "that a bang on the machine, someone jumping up and down on the floor, or even a loud noise can throw us off."
Even the walls of the NanoLab are designed to eliminate vibrations. The floor-to-ceiling windows have two layers of glass to help insulate the lab from the noise that people make just walking by.
The measurements are tiny, but the results may be big. Nanomaterials will likely have a major impact in the design of computers, cellphones, and many tiny machines that can be used to improve our daily life.